AL1 is Aggregate Link number 1.... this is a process of "trunking" multiple ports together logically to create a trunk between switches. This allows you to increase your bandwidth with little or no cost.
How to: on main or core switch, define AL1 as having 2 ports, lets say ports 1 and 2.
On downstream switch, also define AL1 (doesn't matter if it is AL1 or 2,3,4) and include in it 2 ports on that switch, lets say ports 23 and 24.
Now connect port 1 --> 23 and port 2 --> 24
You now have 200meg (or 2 Gig) link for load balancing and redundancy. If either port/connection drops you will still connect on the other link with no problems.
NOTE: it is best to set this up with the 2 switches DISCONNECTED from each other, avoids loops and such.